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I have a couple of years old PC used for semi-serious gaming. It has an Asus P5QC motherboard with 2x DDR2-800 1GB modules installed, running Vista 32 bit. The graphics card is external with its own RAM. I recently ran into memory capacity problems with a new SW, so I'd like to upgrade. However I have no intention of upgrading to a 64 bit windows version.

A few questions:

  1. I understand from "Increase in Available Memory expected by adding 1Gb RAM to a 3Gb Vista 32 bit system" that adding 2 GB won't give any additional benefit to adding 1 GB. Is that generally true, or is specific to the HW mentioned in that question?
  2. Suppose I want 3GB total. The motherboard has 4xDDR2 slots. Can I add 1xDDR2 module and end up with an odd number of modules? I recall some times when memory modules were supposed to be installed in pairs, but I see no mention of this in the motherboard documentation.
  3. For extra cost I could dump the DDR2-800 RAMs I have and replace them with up to DDR3-1333, as supported by the MB. Would I be able to notice the performance benefit of say, 3 GB DDR3-1333 vs. 3 GB DDR2-800 ?


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  1. It is true. Without 64-bit Windows there is no way to access all 4 GB of memory.

  2. You can add any combination of modules you wish and it will work. However, do note that your motherboard has dual channel support and thus memory would work a little faster if you keep modules paired. Personally I would keep them in pairs.

  3. I would keep to DDR2 since you have memory that currently works and you have free slots. You cannot mix memory on your mother board - it must be either DDR2 or DDR3 - not both at same time. Some performance benefits of DDR3 would exist but I doubt that it would be big difference. I would go for DDR2.

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I'd just clarify point 1 - this is not a Windows-specific issue. This is a limitation of 32-bit architectures, period (barring some kind of address extension). – Shinrai Oct 14 '10 at 14:22
@Shinrai: I specified Windows since author of question is interested in them. It is true that all OSes have same issue. – Josip Medved Oct 14 '10 at 14:50
Right, of course, just stating for posterity in case somebody else needs this answer years down the road. :) – Shinrai Oct 14 '10 at 17:03
  1. That's correct. With a 32 bit OS, you'll only be able to address 3GB of RAM.
  2. I think the "DIMMs in pairs" rule is long gone. It was relevant to old MBs. You can safely use eithe 3 X 1GB, or 2GB + 1GB DIMMs.
  3. You stated above that your MB supports DDR2. I wouldn't put DDR3 in it and anyway, unless it's a new MB, you wouldn't get much of a boost. I suggest concentrating on the real bottlenecks in your system if you want a real boost (like a faster hard drive, or even an SSD).
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Where are you getting the 3 gb limit for 32 bit OS? Unless the motherboard is limiting it the limit for 32 bit Vista is 3 gb. – bacord Oct 14 '10 at 6:22
The 3GB limit is only user space per process; you can still address 4GB, even though you can't access all of the fourth gigabyte of physical memory for other reasons. – Ignacio Vazquez-Abrams Oct 14 '10 at 6:25
it's simple math: the maximum memory address you can reach with a 32bit OS is 3GB. You can easily Google this subject (here's one such link: – Traveling Tech Guy Oct 14 '10 at 6:28
That article says that you can't use all of the fourth gigabyte, not that you can't address more than three. – Ignacio Vazquez-Abrams Oct 14 '10 at 6:43
  1. Memory above 3GB has diminishing returns not because the board only supports 3GB, but because I/O space eats into the addressability of the fourth gigabyte. If the board has a smaller I/O footprint (reduced GART, etc.) then more of the physical memory will be visible.

  2. DDR/DDR2/DDR3 modules transfer 64 bits at a time, and since the data bus of most modern PCs is 64 bits wide there's no requirement to add the modules in pairs. Older modules were only 32 bits wide, so they had to be installed in matched pairs in order to be usable.

  3. Personally I wouldn't bother switching to DDR3, unless I had money to burn.

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